Process for dewatering fine-particle solids suspensions

ABSTRACT

PCT No. PCT/EP93/01297 Sec. 371 Date Dec. 1, 1994 Sec. 102(e) Date Dec. 1, 1994 PCT Filed May 24, 1993 PCT Pub. No. WO93/24798 PCT Pub. Date Dec. 9, 1993Finely divided solids suspensions can be dewatered by adding to the solids suspension a mixed hydroxy ether of the formula   &lt;IMAGE&gt;   wherein R1 is a linear hydroxy alkyl group containing from 2 to 16 carbon atoms with the hydroxyl group on the carbon atom adjacent to the carbon atom with the ether linkage and R2 is a linear alkyl group with 1 to 15 carbon atoms with the proviso that the sum of the total carbon atoms in R1 and R2 is 5 to 17, R3 is a linear or branched alkyl group with 1 to 12 carbon atoms and n is a number of from 1 to 20. The mixed hydroxy ethers are readily biodegradable, generate very little foam and have a low solidification point.

FIELD OF THE INVENTION

This invention relates to a process for dewatering fine-particle solidsdispersions, in which internal hydroxy mixed ethers are used asauxiliaries.

BACKGROUND OF THE INVENTION

Large quantities of fine-particle solids of high water contentaccumulate in numerous branches of industry, for example in mining or insewage treatment plants, and have to be dewatered before furtherprocessing or disposal as waste. For example, the dewatering ofwater-containing hard coal or coke is a central process in thepreparation of coal-based fuels. It is often difficult to keep to theupper limits dictated by the market for the water content of thesematerials, for example because mined hard coal accumulates in veryfine-particle form by virtue of the substantial mechanization ofunderground coal mining. At the present time, around 38% of mine-runcoal consists of fine coal with particle diameters ranging from 0.5 to10 mm; a further 14% consists of very fine coal with even smallerparticle diameters.

RELATED ART

It is known that certain surfactants are suitable as auxiliaries forremoving water from water-containing fine-particle solids suspensions,more particularly quartz sands or hard coals, so that the residual watercontent can be reduced. Surfactant-based dewatering aids of the typementioned above, which have already been described include, for example,dialkyl sulfosuccinates [U.S. Pat. No. 2,266,954] and nonionicsurfactants of the fatty alcohol polyglycol ether type [Erzmetall 30,292 (1977)]. However, these surfactants are attended by the disadvantagethat they foam to a considerable extent which gives rise to seriousproblems, particularly because the water is normally circulated in thepreparation plants.

DE-A1-39 18 274 (Henkel) describes alkyl-terminated β-hydroxyalkylethers, so-called hydroxy mixed ethers, which are obtained byring-opening of α-olefin epoxides with fatty alcohol ethoxylates and areused as low-foaming auxiliaries in the dewatering of solids suspensions.Although good results are obtained with these auxiliaries in thedewatering of solids, they have the disadvantage of unsatisfactorylow-temperature behavior. Crystal formation can occur at temperatures ofonly 15° to 20° C., particularly where the auxiliaries are storedoutside, with the result that the pumpability and flow behavior of theproducts deteriorate and their intended use is thus seriously impaired.

Accordingly, the problem addressed by the present invention was toprovide hydroxy mixed ethers which would show improved low-temperaturebehavior for the same performance properties.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a process for dewatering fine-particlesolids suspensions, in which internal hydroxy mixed ethers correspondingto formula (I) ##STR2## in which R¹ represents a linear hydroxy alkylgroup containing from 2 to 16 carbon atoms with the hydroxyl groupbonded to the carbon atom adjacent to the carbon atom with the etherlinkage; and

R² represents a linear alkyl group containing 1 to 15 carbon atoms, withthe proviso that the sum of the total number of carbon atoms in R¹ andR² is 5 to 17,

R³ is hydrogen or a linear or branched alkyl group containing 1 to 12carbon atoms and

n is a number of 1 to 20,

are used as auxiliaries.

It has surprisingly been found that, by comparison with the knownterminal hydroxy mixed ethers according to DE-A-39 18 274, the internalhydroxy mixed ethers to be used in accordance with the invention showdistinctly better low-temperature behavior, more particularly lowersolidification points, and equally good and, in some cases, evenslightly improved performance properties.

DETAILED DESCRIPTION OF THE INVENTION

Internal hydroxy mixed ethers can be obtained similarly to terminalhydroxy mixed ethers by ring opening of internal olefin epoxides withfatty alcohol ethoxylates or glycols. Particulars of the synthesis canbe found in DE-A1-37 23 323 (Henkel).

Internal hydroxy mixed ethers suitable for use in accordance with thepresent invention are ring opening products of internal olefin epoxidescontaining 6 to 18 carbon atoms with ethylene glycol, diethylene glycoland its higher homologs and adducts of, on average, 1 to 20 mol ethyleneoxide (EO) with 1 mol of a linear or branched primary alcohol containing1 to 12 carbon atoms. Typical examples are ring opening products oftechnical internal C₁₀₋₁₄ olefin epoxides with ethylene glycol,diethylene glycol, isopropyl alcohol-3EO, n-butanol-4EO, n-butanol-5EO,n-octanol-4EO and n-decanol-10EO. It has proved to be of particularadvantage to use internal hydroxy mixed ethers corresponding to formula(I), in which the total number of carbon atoms in R¹ and R² is 9 to 13,R³ is an alkyl radical containing 3 to 8 carbon atoms and n is a numberof 1 to 10.

It is pointed out that technical internal olefins are always mixtures ofvarious isomers, so that the internal hydroxy mixed ethers to be used inaccordance with the invention also include technical mixtures of thevarious position isomers.

Commensurate with their use in accordance with the invention, theinternal hydroxy mixed ethers corresponding to formula (I) must bedispersible in water. It is possible that dispersibility in water maynot be satisfactory in cases where long-chain substituents R¹, R² and/orR³ contrast with low values of the degree of ethoxylation n. However,the required dispersibility in water can readily be achieved byincreasing the value for n within the limits mentioned above.

The internal hydroxy mixed ethers to be used in accordance with theinvention may be used individually. However, it can be of advantage fordewatering certain solids to combine products differing in their chainlength or their degree of ethoxylation with one another to utilizesynergisms of their physicochemical properties. Similarly, it can be ofadvantage to use combinations of the internal hydroxy mixed ethers withother already known ionic or nonionic dewatering aids.

The internal hydroxy mixed ethers to be used in accordance with theinvention support the dewatering of solids suspensions, are readilybiodegradable and are distinguished by low solidification points.Accordingly, they are suitable for dewatering suspensions of varioussolids, such as for example iron ore concentrates, quartz sand, hardcoal or coke. Another important application is the use of the internalhydroxy mixed ethers to be used in accordance with the invention asauxiliaries in the dewatering of solids suspensions accumulating in therecycling of wastepaper, for example in the deinking process or in theflotation of fillers.

In one advantageous embodiment of the process according to theinvention, the internal hydroxy mixed ethers are used in quantities of10 to 500 g, preferably in quantities of 100 to 400 g and morepreferably in quantities of 150 to 250 g, based on the solids content,per tonne solids.

The following Examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES I. Hydroxy Mixed Ethers (HME) Used ##STR3##

                  TABLE 1                                                         ______________________________________                                        Composition and solidification point                                                 Number of                  Solidification                                     carbon atoms               point                                       HME    in R.sup.1 + R.sup.2                                                                     n       R.sup.3 °C.                                  ______________________________________                                        A      12/13      7       n-Butyl  -11                                        B       9/12      5       n-Butyl <-25                                        C       9/12      4       i-Propyl                                                                              <-25                                        D       9/12      4       n-Octanol                                                                             <-25                                        E       9/12      2       n-Butyl <-25                                        F      10/11      1       Hydrogen                                                                              <-25                                        G      12/13      1       Hydrogen                                                                              <-25                                        Z      13         7       n-Butyl  +13                                        ______________________________________                                    

Hydroxy mixed ethers A to G correspond to the invention and wereprepared from internal olefin epoxides. The chain length of the startingepoxide derives from the total number of carbon atoms (R¹ +R² +1). Sincethe olefins used are technical mixtures, the hydroxy mixed ethersaccording to the invention are also mixtures of the various positionisomers.

Product Z is a terminal hydroxy mixed ether based on an α-C_(13/14)olefin epoxide according to DE-A1-39 18 274 and is intended forcomparison.

II. Dewatering Tests in a Bucket Centrifuge

Quartz sand having the following particle size distribution was used forthe dewatering tests:

    ______________________________________                                        <125        μm        2.8% by weight                                       125 to 200  μm       26.4% by weight                                       200 to 315  μm       60.1% by weight                                       >315        μm       10.7% by weight                                       ______________________________________                                    

The tests were carried out in a bucket centrifuge with which relativecentrifugal forces of 15 to 2000 can be achieved. Perforated plates withsieve openings of 0.1×2 mm were used as the sieve lining. The dewateringaids were used in the form of aqueous solutions; all concentrations arebased on the solids content of those solutions.

After the quartz sand had been weighed into the bucket of thecentrifuge, the aqueous solutions of the dewatering aids were added anduniformly distributed. After a drainage time of 1 minute, the solid wasdewatered for 30 s at a rotational speed of 500 r.p.m. The moist solidswere then weighed out, dried to constant weight at 100° C. and theresidual moisture content in %-rel was determined. All the test resultsare averages of double determinations. The results are summarized inTable 2.

                  TABLE 2                                                         ______________________________________                                        Dewatering tests in a bucket centrifuge                                                    Residual moisture [% rel]                                        Ex.    iHME        E = 150 g/t                                                                              E = 250 g/t                                     ______________________________________                                        1      A           5.4        4.3                                             2      B           5.2        4.6                                             3      C           4.9        4.2                                             4      D           6.2        5.3                                             5      E           5.0        4.5                                             6      F           4.8        4.5                                             7      G           5.0        4.7                                             C1     None        7.4        7.2                                             ______________________________________                                         Legend:                                                                       iHME = Internal hydroxy mixed ether                                           E = Quantity of ihydroxy mixed ether in g weighed in per t solids        

We claim:
 1. A process for dewatering a fine-particle solids suspension,which comprises: adding to the suspension from 10 to 500 grams permetric ton of solid an internal hydroxy mixed ether of the formula##STR4## in which R¹ represents a linear hydroxy alkyl group containinqfrom 2 to 16 carbon atoms with the hydroxyl group bonded to the carbonatom adjacent to the carbon atom with the ether linkage and R²represents a linear alkyl group containing 1 to 15 carbon atoms, withthe proviso that the sum of the total number of carbon atoms in R¹ andR² is 5 to 17,R³ is hydrogen or a linear or branched alkyl groupcontaining 1 to 12 carbon atoms and n is a number of 1 to 20,andseparating water from the suspension.
 2. The process as claimed in claim1, wherein the sum of the number of carbon atoms in R¹ and R² is 9 to13, R³ is hydrogen or an alkyl group containing 3 to 8 carbon atoms andn is a number of 1 to
 10. 3. The process as claimed in claim 1, whereinthe suspension comprises at least one member selected from the groupconsisting of iron ore concentrate, quartz sand, coal and coke.
 4. Theprocess of claim 1 wherein the fine-particle solids suspension, isformed in a process for recycling wastepaper.
 5. The process of claim 1wherein R³ is hydrogen.
 6. The process of claim 2 wherein R³ is hydrogenand n is a number of from 1 to
 7. 7. The process of claim 2 wherein R³is an alkyl group containing from 3 to 8 carbon atoms and n is a numberof from 1 to
 7. 8. The process of claim 3 wherein the sum of the numberof carbon atoms in R¹ and R² is 9 to 13, R³ is hydrogen or an alkylgroup containing 3 to 8 carbon atoms and n is a number of 1 to
 10. 9.The process of claim 3 wherein R³ is hydrogen.
 10. The process of claim3 wherein R³ is hydrogen and n is a number of from 1 to
 7. 11. Theprocess of claim 3 wherein R³ is hydrogen or an alkyl group containingfrom 3 to 8 carbon atoms and n is a number of from 1 to
 7. 12. Theprocess of claim 4 wherein the sum of the number of carbon atoms in R¹and R² is 9 to 13, R³ is hydrogen or an alkyl group containing 3 to 8carbon atoms and n is a number of 1 to
 10. 13. The process of claim 4wherein R³ is hydrogen.
 14. The process of claim 4 wherein R³ ishydrogen and n is a number of from 1 to
 7. 15. The process of claim 4wherein R³ is hydrogen or an alkyl group containing from 3 to 8 carbonatoms and n is a number of from 1 to
 7. 16. The process of claim 1wherein the sum of the number of carbon atoms in R¹ and R² is from 12 to13, R³ is n-Butyl and n is
 7. 17. The process of claim 1 wherein the sumof the number of carbon atoms in R¹ and R² is from 9 to 12, R³ is analkyl group containing from 3 to 8 carbon atoms and n is from 2 to 5.18. The process of claim 1 wherein the sum of the carbon atoms in R¹ andR² is from 10 to 13, R³ is hydrogen and n is 1.